Key Engineering Materials Vols. 353-358

Abstract: The static strength and stability of a derrick structure (78.5m high) after its members removed partly are researched. The derrick is modeled by three-dimensional spatial beam elements based on ANSYS. By the static analysis, the strength of the derrick after its member removing partly is larger than that of the original derrick structure since some loads disappear. From the buckling analysis, it can be found that the stability reduces drastically when removing some members.

Abstract: Ti2SnC dispersion-strengthened (DS) copper matrix composites were prepared by hot-pressing method. The changes of mechanical properties of the composites as a function of microstructure were studied. The results demonstrated that the grain size of Cu decreased pronouncedly by incorporating of Ti2SnC, and the strengthening effect was significant. The addition of 5 vol.% Ti2SnC particles to Cu resulted in a near five-fold increase in the yield strength and the tensile strength also increased by 188 MPa. The magnitude of the increase was a function of the change of the microstructure.

Abstract: In present paper effect of alloying elements and strengthening particle on the impact toughness were investigated. Load and energy in the impact tests were also discussed in detail for Ti-2Al, Ti-2Sn,Ti-2Zr, Ti-1Mo and Ti/TiC. Impact tests were carried out at room temperature (293K) and low temperature (83K) using a 300J capacity impact machine. Ti-1Mo, Ti-2Zr,Ti-2Sn alloys exhibit high impact toughness even at low temperature, while Ti-2Al and Ti/TiC only have high toughness at room temperature. At room temperature, general yielding occurred in all the materials, but it occurred only in Ti-1Mo, Ti-2Zr and Ti-2Sn at low temperature. It seemed that strengthening titanium couldn’t affect the elastic energy (Ei) effectively, but bring about more changes to Ep (propagation energy of crack) than to Ei (initiation energy of crack). As for the effect of alloying elements on the impact toughness, it seems to be related to the comprehensive result of the concentration and electronegative property of alloying elements. The interface between the TiC particles and matrix resulted in low toughness, especially at cryogenic temperature.

Abstract: A parameterized 3-D finite element model of the screw conveyor of a decanter centrifuge was established. With the model, stress analyses for the screw conveyor under normal operation conditions were carried out and the influences of the structural parameters were investigated. Orthogonal designs were used to sort out major factors and optimize calculations for the effects of factors on the strength of the conveyor. With the finite element calculation results, four empirical formulas for the strength of the conveyor under different loadings were regressed. By applying stress superposition principle, strength check criteria under normal operation conditions were given which can be used for the design of the screw conveyor.

Abstract: The paper experimentally investigated the change of LF9 properties, including strength at room temperature and 350°C, plasticity and impact toughness, under various heat treatment schedules. Results show that the strength of LF9 decreases and plasticity and toughness increase after secondary aging, with the increase of solid solution temperature. Meanwhile, with the increase of aging time, the strength of LF9 increase and plasticity and toughness decrease. The investigation of optical metallography, TEM and phase analysis indicate that the phenomena are mainly caused by the precipitation of η, γ’and γ’’.

Abstract: The creep behavior of functionally graded material under in-plane bending moment is investigated in this paper. By extending the classic beam theory an analytical model is proposed to predict the distributions of creep strain and creep stress inside the functionally graded material according to the relationship between the inclusion volume fraction and composite creep coefficient. The analytical solution agrees well with the results obtained by the finite element method and the basic knowledge about time-dependent behavior of functionally graded material is achieved to guide its design and fabrication.

Abstract: The surface of K24 superalloy was processed with laser cladding & LSP (laser shock processing). Residual stress in the laser cladding zone by LSP was measured with X-ray stress tester X-350A, and the variational rule of residual stress in the cladding zone by tempering treatment of 8 hours and 16 hours was measured, respectively. The experimental results show that compressive residual stress of K24 superalloy surface by laser cladding & laser shock processing is above -600MPa, which exceeds residual stress by mechanical peening treatment; and there is no clear effect on residual stress by tempering treatment at 600°C for 8 hours and 16 hours, respectively, which can improve fatigue life of K24 superalloy.

Abstract: Large scale Ni-based alloy sheets are prepared by electron beam physical vapor deposition with and without tungsten added into melting pools respectively. Addition W increased vapor rate and decreased compositional transformation during deposition. Chemical constitution of the sheet prepared through tungsten is more similar to that of the ingot. Microstructure of two alloy sheets is observed by scanning electron microscope (SEM) and atom force microscope (AFM). The results show that both of the sheets consist of columnar grains, whose major axes are almost parallel to the normal direction of the sheet. However, the average diameter of grains of the sheet through tungsten is larger than that of the sheet not through tungsten in minor axis direction. Mechanical properties and failure mechanisms of both sheets are studied. Tensile tests are conducted on a number of specimens. Strength, strain-to-failure are estimated under loading condition. The results show that the sheet prepared by EB-PVD through tungsten has a superior strength and an elongation percentage than that of the one prepared without tungsten.

Abstract: In order to validate a procedure for creep rupture tests using small punch specimens, the influences of oxidation on the creep deflection curve, rupture time and ductility of miniature specimens were investigated. Using disc test specimens of 10mm in diameter and 0.5mm in thickness, a variety of small punch creep (SPC) tests for Cr5Mo steel at the condition of 550°C-404N and 650°C-189N under the protection of different Argon flow and in air atmosphere were firstly carried out. Metallographic observations, micro-hardness testing and measurement for these specimens of SPC test were performed. It indicates that the oxidized layer of specimens integrates and the residual thickness of specimens increases, while the hardness of specimens increases with the increment of the Argon flow. Moreover, the different oxidation degrees of specimens with the surface morphology were compared in this paper. The test results show the rupture time of specimens can be effectively prolonged by the protection of different Argon flow.